Recently, the field of coded cards for control of access to buildings, money machines, inventory control, time and attendance records, and guard tour clocking has shown an accelerated growth, largely because of the higher degree of security afforded by the use of cards as opposed to mechanical keys. Keys, as opposed to cards, are easily duplicated and cannot be cancelled if one or more are lost. Moreover, the often needed changes in tumbler patterns coupled with issuance of new keys are very expensive.
Along with the growth of card access techniques has come a proliferation of new card and reader technology. Although the most popular technologies involve the use of magnetics in some form, such as the use of embedded magnets, magnetic sheet material with magnetized areas, a series of embedded square loop magnetic wires, magnetic stripes, a matrix of embedded magnetic shields, etc., other technologies are coming into use such as the use of RF resonance, capacitance coupling, punched holes, and laser-coded spots.
These techniques have a number of limitations based on the relative ease with which an individual can decode the information on the cards and the ability to manufacture the cards with the necessary codes in a repeatable, easily performed, low cost manner. It will be appreciated that the provision of a multiplicity of codes is imperative to establish the singular identity of the particular card and that techniques involving the physical placement of elements within the card structure are prohibitively time consuming and expensive. On the other hand, the utilization of an easily generated magnetic coding is exceedingly easy to read out by virtue of passing the card through a magnetic readout head. Thus, the level of security for the card is diminished by the accessibility to readout of the individual code. Moreover, if magnetic shields are utilized for coding, the card can be X-rayed and duplicated assuming access to blank cards.
One technique involves the use of so-called Wiegand wire in which the cards are coded by the placement of wires. The code is not readily duplicatable because the wire itself is not readily available. One drawback to this technique is that the cards are relatively expensive due to the individual placement of the small wires within the card structure.
Optical coding systems are well known as indicated by the universal product code which is optically interrogated. It will be appreciated that the utilization of this type of code on a card is not only readily visible, but exceedingly easy to duplicate with current techniques. The universal product code does however provide an extremely large number of code possibilities and would therefore be extremely useful as a coding technique were it not for the ready accessibility to the code from the surface of card. Other optical encoding systems include the utilization of spots which are infrared transmissive yet opaque to light in the visible region of the electromagnetic spectrum. The coded areas pass infrared and reject all other light to provide the code. However, it is possible to visually ascertain the location of the infrared transmissive spot, and while these cards are difficult to duplicate, the codes are easily ascertainable.
It is therefore desirable to provide for the manufacture of cards with a simple process for encoding which is difficult to duplicate and which is difficult to read out for the unauthorized user. The card must have a code pattern which is quite well hidden to the naked eye and which involves a code which provides for an added level of security.